Crystallization of it-polybutene-1 (iPB-1) in form 2 from thin films of several tens of nanometers thick evolves a cellular structure composed of single-layered lamellar crystals. The dependences on thickness and crystallization temperature of the structure, namely of the cell width corresponding to the lamellar width, have been examined quantitatively. Temperature dependence of the cell width well agrees with the width of lamellar crystals grown from bulk melt, for the thin films with thickness in the same order in magnitude as the long spacing of crystal-melt stacks in the bulk melt. Crystallization from thin films is self-evidently controlled by mass transport under possible influence of compositions. The correspondence of the growth structures from thin films and from bulk melt therefore suggests the essential role of the gradient field of mass transport for lamellar branching in bulk melt, which eventually evolves polymer spherulites. The dependence of cell width on film thickness reflects the facility of mass transport in thicker melt films and the overgrowth on the single-layered lamellar crystals.